In general, a gas turbine used in a power plant and the like combusts fuels sprayed into the air compressed in a compressor and gains output by guiding the high-temperature, high-pressure combustion gas obtained as a result to a turbine. A basic configuration of such a gas turbine is shown in FIG. 14. A gas turbine 100 is provided with a compressor 102, a combustor 103, and a turbine 101. The combustor 103 is supplied with air compressed in the compressor 102 and fuel gas whose flow rate is adjusted by a fuel flow rate adjusting valve 105, whose degree of opening is adjusted in accordance with the load. High-temperature combustion gas combusted in the combustor 103 is supplied to the turbine and drives the turbine 101 by expanding therein. This driving force is transmitted to a generator 150 to carry out power generation and is also transmitted to the compressor 102 to drive the compressor.
Note that in the case of a single-shaft combined cycle power plant, individual rotational shafts of the gas turbine 100, the generator 150, and a steam turbine 160 are integrally connected.
In addition, the compressor 102 is provided with an inlet guide vane (IGV) 104 at the front side of first-stage blades thereof. The inlet guide vane 104 is for controlling the temperature of exhaust gas from the gas turbine 104 to a target value by controlling the degree of opening of the guide vane at a compressor inlet, thereby changing the amount of air flowing between the inlet guide vane 104 and the rotor blades of the compressor 102 and flowing into the combustor The intake air is given a velocity in a circumferential direction by the inlet guide vane 104 and is introduced into the compressor 102. In the compressor 102, the pressure of the introduced air increases, gaining energy as it passes through multiple stages of rotor blades and stator blades.
Note that the inlet guide vane 104 is constituted of a number of movable blades that are provided in the circumferential direction and that are supported so as to be individually movable; and actuators operated based on driving signals from a controller 110 move these movable blades, thereby adjusting the intake air flow rate and the combustion temperature.
More specifically, the controller 110 has a configuration as shown in FIG. 15 in order to generate an IGV degree-of-opening command 115 for the actuators of the inlet guide vane 104. In other words, it is configured to include a multiplier 11, a table function unit (FX1) 12, a limiter 13, a correction function unit (FX2) 14, and a limit function unit (FX3) 15. Basically, the IGV degree of opening is set based on a function shown in FIG. 16A in accordance with generator output (GT output); however, a GT output correction factor K2 is generated by the correction function unit (FX2) 14 based on a relationship corresponding to the compressor inlet temperature, as shown in FIG. 16B, and the GT output value, referring to the table function, is corrected by multiplying the GT output by the correction factor K2 using the multiplier 11. In addition, the limit function unit (FX3) 15 generates a maximum IGV degree of opening M1 based on a relationship corresponding to the compressor inlet temperature, as shown in FIG. 16C, and the limiter 13 limits the IGV degree of opening generated in the table function unit (FX1) 12 so as not to exceed the maximum IGV degree of opening M1.
Known examples of related arts that control the inlet guide vane 104 of the gas turbine 100 in this way include Japanese Unexamined Patent Application, Publication No. 2003-206749 (Patent Citation 1) and Japanese Unexamined Patent Application, Publication No. 2001-200730 (Patent Citation 2). With an operation method disclosed in Patent Citation 1, the intake air flow rate changes greatly depending on the degree-of-opening range such that when the IGV degree-of-opening range is small, a small change in the degree of opening causes a large change in the intake air flow rate and when the IGV degree-of-opening range is large, a small change in the degree of opening causes almost no change in the intake air flow rate; however, a predetermined intake air flow rate for the output can be ensured, even when the intake air flow rate changes greatly depending on the degree-of-opening range as described above. In addition, Patent Citation 2 discloses an operating method in which the maximum IGV degree-of-opening value, which governs the air amount taken into the air compressor using the air compressor inlet temperature as an input, is governed when the actual output of the gas turbine has some allowance with respect to the planned output value or during partial load operation.
Furthermore, degree-of-opening control of a fuel flow rate adjusting vale 105 is carried out based on a control signal 116 from the fuel controller in the controller 110, and load adjustment is carried out by the fuel flow rate control; however, in the fuel controller, based on a blade path temperature setting value for blade path temperature control, an exhaust gas temperature setting value for exhaust gas temperature control, a governor setting value for governor control, or a load limit setting value for load limit control, the lowest value of these is used as a final control signal for the fuel flow rate adjusting valve 105.
In blade path temperature control, the blade path temperature (the exhaust gas temperature immediately after the final stage of the turbine 101) is measured and is compared with a target value based on a temperature adjustment setting, and the blade path temperature setting value is generated by proportional integration (PI) control. In addition, in exhaust gas temperature control, the exhaust gas temperature (the exhaust gas temperature in the exhaust duct downstream of the final stage of the turbine 101) is measured and compared with the target value based on the temperature adjustment setting, and the exhaust gas temperature setting value is generated by proportional integration (PI) control.
FIG. 17 shows a configuration diagram of a portion that generates the temperature adjustment setting, EXREF, used in blade path temperature control and exhaust gas temperature control. The temperature adjustment setting, EXREF, is generated by adding a constant from a signal generator (SG21) 38, using an adder 37, to an output obtained referring to the temperature adjustment setting function unit (FX10) 30 based on a casing pressure, Pcs.
Furthermore, in governor control, velocity control in the rated velocity range is carried out, for which the rotational velocity of the turbine 101 (the generator 150 connected to the turbine 101) is compared with a target value and the governor setting value is generated by proportional (P) control or proportional integration (PI) control. In addition, in load limit control, limit control for the maximum output during load operation is carried out, for which the output of the generator 150 is compared with a target value, and the load limit setting value is generated by proportional integration (PI) control.
FIG. 18 shows a configuration diagram of a portion that carries out load limit control. A target value, LDREF, is generated by signal generators (SG5) 41, (SG6) 49, and (SG8) 52, the adder 42, a subtractor 43, a function unit (FX21) 44, a low value selector 45, and a rate limiter 46; the output of the generator 150 is compared with the target value, LDREF, by the subtractor 47; and the load limit setting value, LDCSO, is generated by proportional integration control with a PI controller 48.
Furthermore, in the configuration shown in FIG. 14, because the generator 150 and the rotational shaft of the turbine 101 are connected, the load of the power generating facility also fluctuates in accordance with the fluctuation of the system frequency. For example, when the system frequency declines, the rotational speed also drops, and the amount of fuel supplied in a gas turbine power generating facility needs to be increased in order to maintain a prescribed rotational speed. Known examples of related arts wherein operating control is carried out in accordance with the frequency fluctuation in this way include Japanese Unexamined Patent Application, Publication No. 2004-27848 (Patent Citation 3) and Japanese Unexamined Patent Application, Publication No. 2003-239763 (Patent Citation 4). Patent Citation 3 discloses a technique of switching to a control that differs from normal control and that mainly aims to recover the system frequency, when an abnormality is detected in the system frequency. In addition, Patent Citation 2 discloses a governor-free control method for performing adjustment so that the rate of change of the system frequency is kept within a limit.    Patent Citation 1: Japanese Unexamined Patent Application, Publication No. 2003-206749.    Patent Citation 2: Japanese Unexamined Patent Application, Publication No. 2001-200730.    Patent Citation 3: Japanese Unexamined Patent Application, Publication No. 2004-27848.    Patent Citation 4: Japanese Unexamined Patent Application, Publication No. 2003-239763.